Whether to fill the fresh water tank or not to fill, that is the question!

[PeterCK]

We have just bought a brand new 2017 Autotrail Imala 625 and, as this is our first 'proper' motorhome my wife went on one of the recognised motorhome manoevering courses. On the course she was advised NEVER to travel with any water in the fresh water tank as it could make the vehicle unstable and also exceed the weight limit. I must admit that I forgot that and did travel on a winding A road and the van was unstable and the Tyre Pro sensors were going off.

However, the whole essence of a motorhome is to be independent so what do other folks do about fresh water levels?

Cheers

Peter

[StuartO]

I have a 2006 Hymer B674 so it's not the same vehicle but I've travelled with varying water tank (and waste tank) levels and not noticed instability. I feel the weight of the load affecting acceleration but no handling issues. Manufacturer recommended not travelling with more than 70% water on mine and nowadays assumes no more than 20 litres but as you say, enjoying the MH requires water carried with you. 

I suggest you do some experiments and work out how much you can carry within weight and handling limits on you type of MH.  The opinion you were given was just someone's opinion and you should assume that it's anything more than that - and certainly cannot apply to all MHs because they vary widely!

[Don636]

I generally travel with a full tank whenever possible just so we are 'good to go'. Never experienced any stability problems that I am aware of. Doing so probably means that the van is slightly over its 3500kg limit but I am not too bothered and accept the minimal risk of being stopped.

[Don636]

Just had a thought - what about fuel tanks - won't they cause the same sort of instability? Sounds like a lot of nonsense to me.

[Brian Kirby]

There are alternative explanations for what you describe. First, were the tyres at their correct pressures? Second, have you taken your van to a weighbridge and weighed it, including the load on both axles? An overweight, especially tail heavy, vehicle might well exhibit some instability.

 

As regards fresh water tank, I always fill ours, and re-fill when half empty. I have weighed the van in its worst case condition with all reservoirs full, and everything and everyone on board, and it is comfortably within both axle limits, and just under its MAM. It is also occasionally driven empty.

I have done this on three different vans since 2005, and have not experienced any instability at any load condition, on any roads: motorways to mountain passes.

 

I do just wonder if the instructor was thinking of trailer caravans with on-board water tanks, where I can readily imagine some stability issues from water surging around.

[HymerVan]

There are other threads already in this forum about how much water to carry Essentially it depends on your assessment of how much you need and where you are going. For example if you are going to wild camp to the next three days you may want to start off with a full tank but if you are going a long way to a fully equipped site you may wish to travel with only a small amount so that you can use loo make tea or whatever on route then fill up when you get there. You will soon get to know from experience how much water you are using and consequently how much is left in the tank. The water gauges are for guidance only and some are so inaccurate they are just about useless.

 

Carrying water IS significant to your payload. If your payload is say 362kg (see Autotrail website) which does not include options and extras and does not include ANY water and you are carrying 100litres of water that reduces it to 260kg. With a passenger weighing 80kg etc etc you may soon get near the limit.

 

As to instability I can only rely on my own experience in two coach builts and two panel van conversions and I never found water significant to the stability of the van. The extra weight might have taken a tiny bit of the performance/increased fuel consumption but this was not discernible. My experience includes high speed cruising on the autostada where the speed limit is approx 80mph and the traffic moves along at that speed all day long.

Vehicles which carry large amounts of liquid (say 30,000 litres weighing say 30 tonnes) have baffles in their tanks to prevent liquids sloshing about. A friend who was a fire appliance driver in the 1970s said that braking a fire appliance hard was a nightmare because the water surged forward causing instability (the tanks were not baffled because they reduced the speed water could be pumped out) but modern appliances apparently have baffles. They are carrying up to 4 tonnes of water though about 50 times as much as a motorhome.

So personally under normal conditions I very much doubt if stability is an issue. Indeed if you think about it a vehicle so badly designed as to be unstable in normal use would scarcely be fit for purpose.

[Agaric]

The only instability I've had in the MH is when the OH is being driven up and down mountain roads.

[henrypartridge]

Depends where the tank is I guess. Corner of a coachbuilt could be dodgy.

[tonyishuk]

My take is;

 

Have enough water for the loo , if travelling, or day out.

 

Have enough water not to loose the prime of the water pump, otherwise having to rectify the problem could be a pain.

 

Otherwise, the weight saved is better used elsewhere, or a saving on fuel.

 

Rgds

 

Edit. Just to say we carry a litre of fresh water, regularly topped up, for drinking, washing teeth etc

[John Allen]

My 2015 Auto Trail Apache has two blue taps on the underside of the offside rear. I imagine your Imala has the same. One of them has a label "Travel Drain" above it. My understanding is that you are supposed to drain the freshwater down to this level before travelling. I believe it leaves you with about 20 litres. However, when we have been travelling around France we have travelled with the tank full as we had plenty of payload still available on both axles when last checked on the weighbridge. We have the luxury of a large payload as the Apache 700 is built on the Fiat Heavy Duty chassis.

[Tony Jones]

All sounds a bit fussy to me. The Caravan (& MH) Club run these courses, right? Hmmmm....

Payload is important, but as long as you can stay within your weight limit I'd say fill 'er up, you never know when you'll get another chance (especially in the UK!).

And converters put the tank low down for a reason - weight there IMPROVES stability (as long as it's inside the wheelbase, which it normally is).

[Derek Uzzell]

A fresh-water tank’s ‘part drain’ tap just allows the motorhome’s driver to comply with the payload-related formula that the motorhome manufacturer has used in the brochure/owner manual. You don’t HAVE to do it, and it’s hardly eco-friendly to waste, say, 80-litres of water if the motorhome is well within its maximum weight limits when the tank is full.

 

All of my motorhomes had their fresh-water tank above the habitation-area floor and only one (a 1996 Herald) had the tank well-forward and fully within the vehicle’s wheelbase. Locating water reservoirs (fresh-water or waste) as low as practicable and within the wheelbase is desirable, but non-double-floor designs with an internal fresh-water tank will normally have the tank mounted above the floor, and many will have the tank well to the rear of the vehicle and sometimes even behind the rear-axle line. Waste-water tanks are often well behind the rear axle (though my Hobby had its waste-water tank just behind the cab) and low-mounted by necessity because gravity is used to drain water into them.

 

Siting water tanks low down does not improve stability; it just keeps the vehicle’s centre of gravity down. Siting tanks higher up raises the vehicle’s C-of-G, and the higher the C-of-G the greater the potential for instabilty. To minimise potential instability (and maximise performance) drive with minimal water in the fresh-water tank and with the waste-water tank empty.

 

That’s just ‘best practice’ though, and I always re-fill my Rapido’s fresh-water tank to its 120-litre maximum whenever the opportunity arises and it's convenient to do so (essentialy, that means when the water is free and it’s not bucketing down with rain).

[tonyg3nwl]

Hi, when we first got the van, we filled the tank right to the top.

 

After the first couple of outings , I realised that there must be a leak somewhere as when we arrived on site, we seemed to have lost a large quantity

 

On investigation, I found that there was a 2 inch overflow towards the top rear corner of the tank, and obviously the water being sloshed around on the journey, was escaping there.

 

I have now covered the overflow, leaving just a small air vent about 1/8 inch diameter, and this has significantly reduced the loss en route.

 

As far as stability us concerned, we dont have any problems.

 

The waste tank at the rear is always emptied before moving off site, if at all possible, or at least at the next available disposal point, be it aire , or other suitable place., likewise the toilet is dealt with as needed.

 

For holiday, with all clutter, persons, tanks anf food contents,bedding electric bikes and camera etc, we weigh in at 3460 overall and both axels in tolerance.

 

Van is Autocruise Stargazer. On fiat base.

 

Tonyg3nwl

[Derek Uzzell]

PeterCK - 2017-08-28 5:44 PM

 

...the van was unstable and the Tyre Pro sensors were going off...

 

Peter

 

Peter

 

May I ask you for more information about the “Tyre Pro” sensors, please?

 

Do these sensors measure tyre pressure and, if so, are you sure you have got the name right?

[Tracker]

In over 50 years of motor homing we travelled with the tank full whenever we could because we never used sites and we were never exactly sure where we would be that night.

Never once in any of the very many vans we owned did I experience any instability and it may be a new 'charecteristic' based on an over sensitive media, poor layout and design, and inadequate payloads.

For me it is simple, if you are going to a site where you know you can fill up no need to carry water, and if you don't know where you will be keep it as full as you can and top it up whenever the opportunity arises.

[Derek Uzzell]

I remember a motorhome review (probably in MMM) mentioning that the vehicle was inclined to ‘oversteer’ when driven on bendy roads, but I did not think the behavour was oversteer as I knew it, more the pendulum effect of having a long rear overhang and a fair bit of weight behind the rear axle. And my Herald motorhome would make me very anxious when driven in high-wind conditions.

 

An Imala 625 has a big (135-litre) fresh water tank and an 85-litre waste-water tank. I don’t know for sure where the tanks are, but photos suggest that neither is right at the vehicle’s rear, so just carrying a full fresh-water tank should not provoke instabiilty. Depends how one defines "unstable” and how the motorhome is being driven at the time.

 

(I recall discussing motorhome poor handling with someone who had just bought a Herald Templar (like I then owned) and complained bitterly that - compared to his car - the Herald’s handling was atrocious. I asked what car he drove and he replied a VW Golf GTi...)

 

[Tall_Mike]

Generally I fill it up according to likely need, most often run with it 1/2 full and have had no problems, I have never noticed an issue if it's full, 1/2 full or empty or in-between, guess that's down to a relatively torque'y diesel

 

I always empty the toilet before travelling. - it's a 17 ltr Thetford, so that's a possible 17 Kg and empty the waste, I think that's about 90kg, - no need to carry what isn't needed.

 

We are lucky in that we have a 600kg payload - even with the tank full, and in full travelling mode we are just under the limit, - I believe the first 10% of overweight is discretionary, in the unlikely event we did encounter weight problems we would first drain the fresh water which is a whopping 110kg from full and be back under the limit.

 

Some other vans are very tight on the weight limits with little room for manoeuvre, - it would then be a different story.

[tonyishuk]

Another factor is how do you intend to mhome ?

 

If you are freeloading (wild camping) it pays to take water with you.

If you intend to use camp sites, there seems little point in carrying water over the countryside, if there is water in the tap at The end of the journey.

If you are going out for the day, enough to flush the loo is sufficient.

 

As others have pointed out, hidden water in toilet cassettes and waste tanks add to the load if not emptied.

 

The choice is yours , and that is what mhoming is about.

 

Rgds

 

 

 

 

[Bop]

PeterCK - 2017-08-28 5:44 PM

 

We have just bought a brand new 2017 Autotrail Imala 625 and, as this is our first 'proper' motorhome my wife went on one of the recognised motorhome manoevering courses. On the course she was advised NEVER to travel with any water in the fresh water tank as it could make the vehicle unstable and also exceed the weight limit. I must admit that I forgot that and did travel on a winding A road and the van was unstable and the Tyre Pro sensors were going off.

However, the whole essence of a motorhome is to be independent so what do other folks do about fresh water levels?

Cheers

Peter

 

Hi Peter,

 

We've just sold our 66-plate Imala 620 Hi-Line so the points you make are quite familiar with myself and Mrs Bop.

 

All in all we found the Imala @ 6.34m in length to be a great van and highly usable due to its size and general versatility.

 

We would usually run with 56-litres in the freshwater tank and this made for good driving conditions where on most road surfaces the chassis would cope incredibly well with that kind of water loading. That said, on the two occasions we ran with full fresh water then the road handling changed massively and we found the van forcing itself into the corners (the water tank is on and behind the rear axle). This was easily rectified by me slowing down and then driving within the new limitations set - it makes sense eh

 

One point that you need to consider (as mentioned by the chaps above) is payload.

 

The manufacturers quoted MIRO on the Imala 620 is 3005kg whereas yours is 2980kg but please don't assume that this figure is entirely accurate.

 

Our Imala was registered at 3,500kg but when we visited the council weighbridge we came in @ 3,600kg with full fresh water, hence the reason why the road handling became challenging when the van was fully kitted-out.

 

Note: Our spec for the weighbridge was: Full fuel, full fresh water, bike rack and two mountain bikes, solar panel, Media Pack-1, skinny wife, Awning, our gear.

 

I pondered over my weights a few times and finally came to the conclusion that my MIRO figure was circa 3,140kg and not 3,005kg as stated in the shiny brochure. This is the bit that tipped me over the scales!

 

Hope this helps,

 

All the best,

 

Andrew

[ron.]

In over 50 years of motorhoming I had never heard of this 20 litre fresh water limit whilst driving until recently.. Now it comes up regularly. Is it just a coincidence that without this 'advised' limit many new motorhomes would have such a poor payload as to be next to unusable? In other words manufacturers who can no longer build models down to a decent weight, usually 3500, have adopted the 20 litre rule simply to get round a problem. What next, do away with the washroom and only use campsite facilities?

 

We are supposed to be enjoying ourselves and not faffing about dumping water water every time we move.

 

Ron

[Derek Uzzell]

Ron

 

When I started motorcaravanning in 1998 UK motorhome converters quoted their vehicles’ Mass In Running Order (MIRO) just with allowances for a driver (75kg) and a full fuel tank.

 

France, however, was using a weight-related formula to define how many people a motorhome could legally carry and that datum appeared on the vehicle’s ‘registration certificate'. The formula included allowances for a driver, fuel, fresh-water and a gas bottle to produce a MIRO value. That value was then subtracted from the motorhome’s Maximum Authorised Mass (MAM) and the result divided by 75kg to produce a number-of-passengers datum. This often meant that motorhomes marketed in France had much smaller fresh-water tanks than the same models marketed elsewhere (and, just to complicate matters furher, the French Highway Code allowed passengers under 10 years of age to be classed as ‘half adults’, permitting, in principle, a motorhome able to legally carry three adult passengers to carry six under-10 children instead).

 

Some standardisation came with the publication of Euro-Nom EN 1646-2 that specified the method of calculation of minimum user payloads to be allowed for when designing motor caravans. It also set out the information relating to user payload to be included in the user´s handbook. This produced a more realistic user-payload figure, but there were still pitfalls for the unwary as this 2008 forum discussion highlights

 

http://forums.outandaboutlive.co.uk/forums/Motorhomes/Motorhome-Matters/Payloads/10827/

 

More recently motorhome converters began to specify fresh-water capacity using two values, with one value indicating the fresh-water tank’s maximum capacity and the other being a lower figure for when the vehicle is being driven.

 

I have 2016 Rapido brochures and one (for “Van” models) defines the fresh-water capacity as 110/50, whereas the other (for ‘coachbuilt’ models) defines the capacity as 120/20, 130/20 or (for Series 10 models) 300. When the tank capacity is expressed as a maximum/lower datum, there’s a footnote that the tank can be filled to the maximum value which will result in a lower payload.

 

2016 Hobby motorhome brochures define the MIRO as the weight of the empty vehicle, including lubricants, on-board tools,repair kit, fuel (90%), extra battery, all standard factory-fitted equipment and 75kg for the driver, with an allowance of 120kg for fresh-water and gas-containers. The fresh-water capacity is given as a single ‘tank maximum’ value.

 

The 2016 Knaus motorhome brochure defines MIRO as

 

- Tare weight of vehicle (including tool kit)

+ diesel tank 90% full

+ 75kg (driver’s weight)

+ liquid gas bottle 100% full

+ fresh water tank 100% full (capacity limited to 20 litres fresh water in driving operation, when technically planned)

+ toilet flush tank 100% full

+ fresh water heater tank 100% full

 

and there’s a footnote saying

 

“The capacity of the fresh water tank can be limited to 20 litres with an oveflow valve according to Annex V. Part A, Sec. 2.6 Fn (h) V0 (EU) 1230/2012 (recommended filling when driving).”

 

(EU) 1230/2012 can be viewed here

 

http://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32012R1230&from=en

 

(and the best of luck!)

 

The situation seems to be that - as long as the motorhome converter makes it clear in their documentation - they can specify two fresh-water capacities, one RECOMMENDED for travelling and a higher capacity (the tank’s maximum) for when the motorhome is static.

 

I don’t know whether a zero lower-capacity figure can be given (I believe I’ve read somewhere that there’s nothing stopping a converter doing this) but 20 litres is probably a realistic minimum. I’m pretty sure that, when the two-capacities approach began to be used, the fresh-water tanks did not all have a secondary drain valve, so reducing the amount of water to the while-travelling recommendation would have relied on the tank’s contents-level gauge being accurate (or on guesswork).

 

As you suggest, I would have thought that the primary reason for a motorhome converter choosing to specify a recommended while-travelling fresh-water datum is to improve the vehicle’s potential user-payload, as payload only becomes significant when the vehicle is being driven.

 

Minimising a motorhome’s weight will always be beneficial when the vehicle is being driven and - simply as a generalisation - driving with a full fresh-water tank COULD lead to instability in the case of some motorhome designs.

 

Andrew (Bop) has mentioned that his Auto-Trail Imala 620’s handling was OK with 56 litres (that’s very specific...) in the fresh-water tank, but changed its behaviour significantly when the tank was full. The Imala 620 has a relatively short (3.45m) wheelbase, and its fridge, kitchen, bathroom and fresh- and waste-water tanks are all positioned behind the rear-axle line. With that specification, adding an extra 79kg of weight at the rear by upping the fresh-water from 56 litres to 135 litres clearly has plenty of potential to adversely affect the handling.

 

The Imala 625 has the same shortish wheelbase as the 620’s, but has a rear U-lounge layout with its fridge, kitchen and bathroom much further forwards and within the model’s wheelbase. The fresh-water tank filler’s position suggests that the tank is still behind the rear-axle line, but I’d expect the waste-water tank to be beneath the kitchen/bathroom. On paper, then, an Imala 625’s weight distribution is a good deal better than a 620’s and one might expect the affect on handling of having a full fresh-water tank to be a good deal less.

 

Without knowing the loaded condition of Peter’s 625 when it exhibited instability (eg. how much ‘stuff’ was under the rear seats, were there bikes on the back and (as Brian has asked) what tyre pressures were being used?) it’s not really possible to guess why a full water tank made the vehicle turn nasty. I could easily imagine an Imala 620 becoming wayward, but not an Imala 625.

 

 

 

 

[Brock]

This MMM news item briefly explains why the change to the fresh water figure was brought in:

 

https://www.outandaboutlive.co.uk/motorhomes/news/european-rule-changes-means-more-motorhome-payload

 

I've always thought the MMM heading was a bit misleading. My Hymer has the 20l valve although I've never used it. Since increasing the available payload, I tend to travel with between 30l and 65l in the fresh water tank - located in front of the rear axle - because the van seems more settled on the road. As Derek says, it lowers the centre of gravity.

 

Historically, double deckers have been designed to tilt at 28%. I have a feeling its 35% for single deckers. We need someone to test how far a motorhome tilts before it tips over ...

[Derek Uzzell]

Ah yes, I thought I’d read something Out&AboutLive-related about water capacity definition changes, and I note it was discussed on this forum in 2015

 

http://forums.outandaboutlive.co.uk/forums/Motorhomes/Motorhome-Matters/Is-it-just-me-/39893/

 

and, more recently, was mentioned here in this 5-page thread

 

http://forums.outandaboutlive.co.uk/forums/Motorhomes/Motorhome-Matters/Worried-about-payload-on-Apache-632/46654/31/

[Tracker]

Brock - 2017-08-30 10:47 AM

 

Historically, double deckers have been designed to tilt at 28%. I have a feeling its 35% for single deckers. We need someone to test how far a motorhome tilts before it tips over ...

 

That sounds like fun, can I watch please!!

 

You may need to do it several times, once tanks empty, once tanks full and once tanks half full, or half empty depending whether you are an optimist or a pessimist!!

[RogerC]

Overweight considerations I can agree with but 'instability'??  Seems to me another case of H&S gone mad.  If anyone is so 'sensitive' to weight shift because of 70 or so kg of water I reckon it's best you never travel with anything but a full or near empty fuel tank (just imagine all that slopping about.....).......full is around 85-90kgs depending on base vehicle, additions to the MH in terms of foodstuff/wine/beer etc etc etc also alter the dynamics as well so I reckon it's load of old cod's..... :-)